California health officials confirmed a fourth-ever human case of Rickettsia lanei, a rare tick-borne illness with symptoms similar to Rocky Mountain spotted fever. The patient was hospitalized, has been discharged, and is recovering.
A Northern California patient was hospitalized after being diagnosed with a newly recognized, rare tick-borne disease that health officials say resembles Rocky Mountain spotted fever—an illness they note is caused by bacteria transmitted through tick bites.
The California Department of Public Health confirmed the latest case of Rickettsia lanei bacteria in April of this year. making it the fourth-ever person diagnosed worldwide. The state said the infected person “was seriously ill. hospitalized and has since been discharged and is recovering.” Public health officials also said it is unclear how long the person was hospitalized or what their symptoms were. The agency would not disclose the home county, but it confirmed the person lived and worked in Northern California.
Rickettsia lanei belongs to the spotted fever group of Rickettsia bacteria. Like other spotted fever–type infections, it can be transmitted to humans through the bite of an infected tick. In California. the California Department of Public Health said three types of ticks— the American dog tick (Dermacentor similis). the Pacific Coast tick (Dermacentor occidentalis) and the brown dog tick (Rhipicephalus sanguineus)—can transmit the bacteria that cause Rocky Mountain spotted fever in humans and dogs.
For many people, that overlap matters. Rocky Mountain spotted fever symptoms can range from fever and a rash to long-term effects including damage to internal organs or neurological disorders.
The disease has been spreading globally since the early 2000s, most notably in Mexico and Brazil, and a study published by UC Davis says reported fatality rates can exceed 50%.
What researchers and health officials already know about Rickettsia lanei
California has now recorded two other human cases besides this April diagnosis—one reported in 2004 and another in 2023.
The bacterium itself was added in 2024 to the state’s list of potentially transmittable pathogens after severe symptoms were studied in two cases of infected men nearly 20 years apart. according to a report published in the Centers for Disease Control and Prevention Emerging and Infectious Diseases journal.
In the first of those earlier cases, the report says the man fell ill after spending time outdoors. He played golf at five courses in Alameda and Contra Costa counties within 14 days of the onset of his symptoms. The report lists symptoms including fever, headaches, muscle pain, malaise, loss of appetite, diarrhea and abdominal pain. His condition worsened on his third day in the hospital.
That patient ultimately spent 22 days in the hospital, including 11 in the intensive care unit, with a primary diagnosis of rocky mountain spotted fever and a secondary diagnosis of acute kidney injury.
The second earlier case described in the CDC report involved another man who visited and camped at a county park and a state beach in San Mateo and Marin counties. The report says he had a five-day history of headaches, vomiting, light sensitivity, neck pain and confusion. On the third day of hospitalization, he became comatose and was intubated. After 13 days, he was discharged with a primary diagnosis of severe Rickettsia.
The state health agency has also pointed to how humans may rarely be exposed. The California Department of Public Health said researchers have known about Rickettsia lanei since 2018. when it was detected in rabbit ticks in Sonoma County. but they did not know its potential harm to humans because the rabbit tick rarely bites people.
“The Pacific Coast tick, which bites humans more frequently, may occasionally acquire the organism from an infected rabbit, which is the most likely route for the rare human infections that have been identified,” the state health agency said.
Ticks carrying the bacteria have been found in recent years as well. The report says the bacterium was identified this year in a few Pacific Coast ticks, including a tick in Contra Costa County, according to SFGate, where the latest case was first reported in April.
Public health officials emphasized they are improving detection. In a statement to The Times, the California Department of Public Health said: “Sustained investment in public health has enabled development of the advanced molecular tools that detected these infections.”
How worried should Californians be?
Human infections are rare, but UC Davis veterinarian and disease ecologist Janet Foley said the illness could be underreported because Rickettsia lanei symptoms are very similar to those of rocky mountain spotted fever.
“I think it’s so new that I don’t know if anybody’s really gotten a grant to study it or put it under a microscope,” Foley said. She added that some cases might have gone undetected for so long because not every illness is severe.
For Foley, the takeaway for residents is straightforward: be aware of the possibility of tick-borne disease and protect yourself against tick bites.
How to reduce your risk of tick bites
Foley recommended that Californians stay vigilant, noting that ticks can transmit other diseases such as Lyme disease. To avoid ticks and tick bites, she recommended:
Covering up arms and legs outdoors by wearing pants and long-sleeved shirts.
Staying out of the grass where ticks can latch onto clothing, and instead using cleared paths.
Wearing light-colored clothing so ticks are easier to spot if they land.
After an outdoor activity, taking off clothes, tossing them in the wash, and taking a shower.
If a dog goes on outdoor activities, giving it a bath and then applying tick medication.
For now. health officials are asking residents to watch for ticks and take prevention seriously—not because Rickettsia lanei is common. but because when tick-borne illnesses look like something else. the wrong assumptions can delay treatment. And in this case. the patient’s recovery after serious hospitalization is a reminder of how quickly the stakes can rise once an infection takes hold.
MISRYOUM California public health tick-borne disease Rickettsia lanei Rocky Mountain spotted fever UC Davis tick prevention